ISWA: Start for biorefinery project to recover raw materials from wastewater

Scientists from the University of Stuttgart, the DVGW Research Unit at the Engler-Bunte Institute of the Karlsruhe Institute of Technology (KIT), the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB), the Technical University of Hamburg and the Clausthal University of Technology are working together with Umwelttechnik Baden-Württemberg (UTBW) and the State Agency for Environmental Technology and Resource Efficiency, on a project on new processes for wastewater treatment. The KoalAplan project („Kommunales Abwasser als Quelle für Ammoniumstickstoff, Wasserstoff und Bioplastik – die Bioraffinerie Büsnau“/Municipal wastewater as a source of ammonium nitrogen, hydrogen and bioplastics - the Büsnau biorefinery) aims both to recover raw materials from municipal wastewater and to make a positive contribution to climate neutrality.

In a classic wastewater treatment plant, the nitrogen compounds contained in the wastewater are converted by microorganisms into gaseous nitrogen, which escapes unused into the atmosphere. For this, they require organic carbon, which is accordingly no longer available as a raw material, but is discharged as CO₂ and sewage sludge.

"We bypass biological nitrogen removal in our project and want to show that we can recover a large part of the organic load from wastewater," says Prof. Dr. Harald Horn, head of the DVGW research unit and professor at KIT.

The planned process concept consists of chemical, physical, and biological process steps. A core element of the entire process is the use of microsieves to separate the particulate organic carbon from the wastewater stream already after primary clarification. In the main stream process, the ammonium nitrogen is subsequently removed by means of ion exchangers, producing a product that can be used as a fertilizer. In the side stream process - the actual biorefinery - the filtered solids as well as the primary sludge are first converted into organic acids by acid hydrolysis (dark fermentation), which also produces biohydrogen and CO₂. The hydrolysate is then filtered and converted to hydrogen (and again CO₂) by microbial electrolysis. Hydrogen has many applications in the chemical industry and is considered a future energy carrier. In a feasibility study, the gas streams from microbial electrolysis and dark fermentation are utilized in a biotechnological process for the production of valuable chemicals; in the process, the carbon dioxide contained is also re-fixed.

Die Stoffströme, die u. a. Carbonsäuren enthalten, werden in einem Fermentationsverfahren zu Polyhydroxyalkanoaten (PHA), einem natürlichen Biopolymer, umgesetzt. "Aus Abfallstoffströmen stellen wir das mikrobielle Biopolymer PHA her, ein Ausgangsmaterial für biologisch abbaubare Verpackungsmaterialien und können damit persistente Kunststoffe aus fossilen Quellen ersetzen", so Dr.-Ing. Susanne Zibek, Gruppenleiterin Bioprozesstechnik am IGB.

 

The material streams, which contain carboxylic acids and other substances, are converted in a fermentation process to polyhydroxyalkanoates (PHA), a natural biopolymer. "From waste material streams, we produce the microbial biopolymer PHA, a starting material for biodegradable packaging materials and can thus replace persistent plastics from fossil sources," said Dr.-Ing. Susanne Zibek, group leader of bioprocess technology at the IGB.

The new process concept is being tested at the University of Stuttgart's Sewage Treatment Plant for Research and Education (LFKW), which is part of the faculty's  (LFKW) at the Institute for Sanitary Engineering, Water Quality and Solid Waste Management (ISWA) of the Faculty. Dipl.-Ing. Peter Maurer, Technical Operations Manager of the LFKW: "In Büsnau, we are testing innovative processes for wastewater treatment. We've often had to go against prevailing opinion, but have usually been rewarded with success."

The project is also investigating what other effects the innovations will have. "A detailed life cycle assessment will show whether we achieve a positive contribution to the environment and the climate with the process," says Dr. Andrea Hille-Reichel, project manager at KIT. With the help of a climate and energy balance, the process can be compared to the classic wastewater treatment plant operation.

"We are networking the local players and looking for regional buyers for the generated products. We are convinced of the market potential and economic viability of the process," says Dr.-Ing. Anette Zimmermann, head of the environmental technology team at Umwelttechnik BW.

The KoalAplan project is designed to demonstrate the potential for recycling in wastewater treatment. The projected recovery of the products hydrogen, bioplastics and nitrogen/phosphorus fertilizer can significantly reduce current resource consumption. In parallel, energy-intensive processes will be replaced and emissions reduced. Therefore, the project was awarded by the ministry as an important part of the state strategy "Nachhaltige Bioökonomie für Baden-Württemberg" (Sustainable Bioeconomy for Baden-Württemberg.

With this state strategy, the state government supports the change to a raw material-efficient and cycle-oriented economy based on renewable and biological resources. This serves to protect our natural resources and strengthens Baden-Württemberg as a business location.

The project is funded by the ministry as part of the ERDF funding program "Bioökonomie – Bioraffinerien zur Gewinnung von Rohstoffen aus Abfall und Abwasser – Bio-Ab-Cycling" (Bioeconomy - Biorefineries for the recovery of raw materials from waste and wastewater - Bio-Up-Cycling).